An oil containing LC-PUFAs such as for example arachidonic acid (ARA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) or dihomogammalinolenic acid (DHGLA) may be obtained from a biomass fermentation broth. To obtain the oil from the biomass, methods of extraction with organic solvent, for example hexane, or with supercritical fluid, have been used. Generally, the oil has been extracted from biomass by percolation of the dried biomass with hexane.
Such a process of extraction with organic solvent(s) is described, for example, in WO9737032, in WO 9743362 or in the publication Journal of Dispersion Science and Technology, 10, 561-579, 1989 “Biotechnological processes for the production of PUFAs”.
This technique has various disadvantages:                During the stages of extraction with hot solvent or of distillation of the solvent, the LC-PUFAs may undergo degradation in contact with oxygen.        The complete removal of the solvent contained in the oil or in the residual biomass requires a heat treatment at high temperature.        Moreover, the solvent, such as hexane, is capable of dissolving nontriacylglycerol constituents of the biomass which in fact constitute impurities.        
The crude oil obtained after evaporation of the solvent should further undergo several refining stages comprising degumming, neutralization with alkali, decolorization, dewaxing and deodorization with the aim of at least partially removing the impurities. This means that the highly unsaturated oil is exposed to conditions stimulating physicochemical reactions which affect its quality. For example, the decolorization agents create a system of conjugated double bonds and form degradation products by chemical reaction with the oxidized glycerides.
A process for extracting biomass with no solvent is also known, for example from EP-A-1178118. According to this process, the use of solvent is avoided by preparing an aqueous suspension of the biomass and by separating an oily phase, containing the desired oil, from the aqueous phase, by centrifugation. The aqueous phase contains cell wall debris and a quantity of water-soluble material obtained from the biomass. A disadvantage of this process is that the crude oil obtained is contaminated with quantities of impurities, for example polar lipids, residues of proteins due to the presence of water. Such a crude oil should then be refined by conventional methods for refining vegetable oils.
The aim of the present invention is to avoid the disadvantages of the prior art, by providing a process for preparing a stable oil containing one or more polyunsaturated fatty acids derived from biomass in the form of triacylglycerols in the purified state with a high yield and in which the oil undergoes minimum degradation.